This invention concerns an improved system for measuring the temperature of food loads being cooked in a microwave oven.
Metal probes that are inserted directly into the food as it cooks are commonly employed to measure its temperature; these probes have a metal sheath and flexible coaxial cable leads. One problem with metal probes is sparking, which can leave a carbon deposit on the food where it plugs in; if the probe is left on the floor of an empty oven with the power on, there can be a great deal of sparking. Another problem is that the metal sheath concentrates the microwave field in its vicinity and causes local heating. There is an error in the reading even though the local heat diffuses into the food.
Electric probes which are uniquely electric and magnetic probes which are uniquely magnetic are described in concurrently filed application Ser. No. 28,179, and are constructed with leads of electrically conductive iron oxide magnetic tape having a high resistance per unit length that are transparent to electromagnetic fields. Electric potential differences are conveyed to electrometers or control devices with minimal perturbation of the waves and without altering the elemental electric and magnetic probes.